This application claims priority to German Patent Application Nos. 10140372.0 filed Aug. 23, 2001 and 10204684.0 filed Jun. 2, 2002, which applications are herein expressly incorporated by reference.
The invention relates to a cross member unit for universal joints having a cross member with four trunnions. Each two of the trunnions have a common longitudinal axis. A bearing bush, per trunnion, supports the trunnions via rolling members. A sealing assembly, per bearing bush, effectively seals between the bearing bush and the trunnion. The sealing assembly ensures that lubricating grease for the rolling members cannot leave the bearing bush.
DE 196 22 444 C1 discloses a cross member unit. A main seal with a carrier is firmly positioned in an open end of the bearing bush. The carrier, to provide axial security, is formed into an annular groove which is arranged coaxially relative to a longitudinal axis of the trunnion. The main seal has two sealing lips which are formed onto the carrier. The lips are in sealing contact with sealing faces of the trunnion. The carrier projects axially from the open end of the bearing bush. A pre-seal is firmly slid onto a seat portion of the trunnion. The cross-section of the pre-seal has a U-shaped profile which embraces the projecting carrier of the main seal. A sealing lip is provided at one radially outer limb of the U-profile. The sealing lip is in sealing contact with a conical face of the bearing bush. A further sealing lip is in sealing contact with the metallic carrier of the main seal. The two sealing lips of the pre-seal ensure that even under the influence of a water jet of a high-pressure cleaning device, dirt cannot easily enter the region of the main seal. However, the pre-seal sealing lip which stops against the conically shaped sealing face of the bearing bush is directly subjected to external influences. In addition, it is necessary to provide two separate seals. Furthermore, the cross member unit according to DE 196 22 444 C1 has a stop disc between the main seal and the rolling members. The stop disc axially supports the rolling members.
It is an object of the present invention to provide a cross member unit for universal joints which includes a sealing assembly with a small number of parts. Also, the trunnion is stronger with respect to its diameter.
In accordance with the invention, a cross member unit for universal joints has a cross member with four trunnions. Each two trunnions define a common longitudinal axis. Each trunnion has an end face, a first sealing face and a pre-sealing face. The pre-sealing face is remote from the end face. The diameter of the pre-sealing face is increased relative to the first sealing face. A bearing bush is present per trunnion. The bearing bush has an open end and rotatably supports, via rolling members, the trunnion around the longitudinal axis of the trunnion. An annular seal is provided per bearing bush. The annular seal is held in the bearing bush by a press-fit. The annular seal includes an annular carrier which projects from the open end of the bearing bush. The annular seal includes at least one first sealing lip which is in contact with the first sealing face of the trunnion. The annular seal includes a pre-seal in the form of a sealing lip or bead which is in contact with the pre-sealing face of the trunnion. An end face of the carrier, remote from the end face of the trunnion, forms an annular gap together with a radial face of a shoulder of the trunnion. The cross member unit includes only one seal with at least one first sealing lip which acts as a main seal, and a pre-seal, in the form of a sealing lip or bead, which prevents dirt from penetrating into the region of the first sealing lip.
There is no need to provide a seat portion on the trunnion so that the pre-seal is in contact with a pre-sealing face of the trunnion. The diameter of the pre-sealing face of the trunnion can be greater than the diameter of a seat portion for a separate pre-seal. This means that the trunnion is reinforced in the critical region where the highest stresses occur. Since only one seal is provided, which is inserted into the open end of the bearing bush, the number of necessary assembly stages is reduced.
Furthermore, there is no need to provide a sealing face at the bearing bush. Thus, the bearing bush can be produced more easily and more cost-effectively. Further, it is not necessary to provide an inner circumferential groove in the bearing bush. The groove receives the carrier to axially secure the seal. The axial distance which the seal can be displaced inside the bearing bush, due to external forces, is delimited by the rolling members and by the radial face of the shoulder of the trunnion. In addition, the press fit ensures that, under normal loads, the seal is firmly positioned inside the bearing bush. The annular gap between the seal carrier and the radial face of the trunnion shoulder is dimensioned to compensate for any tolerances in the axial length of the seal and in the length of the rolling members. Therefore, in extreme case, the width of said annular gap can assume a zero value. The carrier can be metal or plastics, such as PA 6.6 for example.
Furthermore, the annular gap acts as a labyrinth seal. Thus, the pressure of a water jet of a high-pressure cleaning device is reduced when the water jet enters the annular gap. The pre-seal is protected by the carrier from direct external influences.
To increase the sealing effect, the seal may include a second sealing lip. The second sealing lip is in contact with a second sealing face of the trunnion. The second sealing lip is arranged in the direction of the longitudinal axis of the trunnion between the pre-seal and the first sealing lip. The first sealing lip and the first sealing face are designed so that the first sealing lip is pressed radially against the first sealing face. The second sealing lip and the second sealing face are designed so that the second sealing lip is axially pressed against the second sealing face.
In addition, it is possible to provide a third sealing lip. The third sealing lip is in contact with a third sealing face of the trunnion. The third sealing lip is arranged between the first sealing lip and the second sealing lip.
The carrier includes a radial annular portion to eliminate a stop disc between the seal and the rolling members. The radial annular portion remote from its end face includes a stop face for the rolling members which faces a way from the end face. The annular portion of the carrier thus takes on the function of a stop disc. The stop face includes a friction-reducing coating to reduce the friction between the radial annular portion of the carrier and the rolling members. Accordingly, since there is no need for a stop disc, the rolling members can be longer. Thus, the rolling members length prolongs the service life of the rolling member bearing.
The cross-section of the radial annular portion can be convex towards the rolling members. The rolling members, in the region of their axis of rotation, stop against the radial annular portion.
An outer seal is circumferentially secured to an outer face of the carrier portion to prevent any spray water from entering the region between the carrier of the seal and the bearing bush. The outer seal projects from the open end of the bearing bush. The outer seal is in sealing contact with an outer sealing face of the bearing bush. The outer seal effectively prevents spray water from entering the region between the carrier and the inner circumferential face of the bearing bush even when the universal joint is cleaned by a high-pressure cleaning device.
In a preferred embodiment, the outer sealing face includes a chamfer. The chamfer starts from an end face at the open end of the bearing bush and extends to an inner circumferential face of the bearing bush. The outer seal is in sealing contact with the chamfer.
The outer seal includes an outer sealing lip to increase the sealing effect of the outer seal. The sealing lip is in contact with the outer sealing face of the bearing bush. The outer sealing face may include an end face at the open end of the bearing bush. The outer seal is in sealing contact with the bearing bush.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.